Air cushion stability control device with adjustable plenum chamber volume



Sept. 12, 1967 R. R. HIRSCH AlR CUSHION STABILITY CONTROL DEVICE WITH ADJUSTABLE PLENUM CHAMBER VOLUME 2 Sheets-Sheet 1 Filed May 4, 1966 p 12, 1967 v R. R. HIRSCH 3,340,943

AIR CUSHION STABILITY CONTROL DEVICE WITH ADJUSTABLE PLENUM CHAMBER VOLUME Filed May 4, 1966 2 Sheets-Sheet 2 Fl'g :4

United States Patent 6 8 Claims. icl. 180-7) Fluid cushions, which are generally used to support a vehicle but sometimes also to guide one show a certain amount of resilience in the movements of the vehicles perpendicularly to the support surface with which they 00- operate. The compressor feeding such a cushion and the retaining means limiting the rate of leakage of the carrying fluid at the periphery of the cushion form simple pressure barriers through which the fluid constantly passes; the compressibility of the fluid must, therefore, be taken into account if it is gaseous, and so must the elasticity of the retaining means, comprising flexible skirts and/ or fluid curtains. Some cushions are dynamically unstable, at least in some operating conditions, and it is desirable to have cushions which are quite stable in any circumstances, for example to prevent the vehicle from responding too violently to resonance-frequency influences.

This invention relates generally to a combination with the assembly of means defining a fluid carrying cushion of a device enabling the'natural stability of the cushion to be modified by action on the volume provided for it.

The invention relates particularly to devices increasing the natural stability of a cushion by varying the volume of the cushion in inverse proportion to the natural variations of the volume which are associated with chance variations of the intern-a1 pressure of the cushion.

The invention also relates to devices providing a fluid cushion or fluid-cushion vehicle with shock-absorption characteristics other than their natural ones, so that, for example, a mock-up dynamically similar to a projected cushion or vehicle can be produced and the future -behavior of the vehicle in question studied on the mock-up, whose characteristics can be modified very easily within a wide range extending to the limits of instability.

According to the invention, a fluid cushion, the characteristics of which are to be modified, conventionally confined by any lateral retaining means and by a top, pref- .erably a practically inextensible wall, is combined with a deformable element, means being provided so that the element is deformed by varying the volume of the cushion when the distance between the wall and the bearing surface and/ or the internal pressure of the cushion vary.

The deformable element whereby the volume of the cushion can be varied is in direct communication, i.e. substantially without loss of pressure, with the cushion. The elements forming the deformable element are controlled, at least indirectly, by at least one parameter connected with the internal pressure of the cushion.

These elements include at least one elastic diaphragm, a piston sliding in a cylinder, a flap associated with a bellows and pivoting in a recess of a wall of the cushion, and any possible combinations of the elements just given as examples.

These elements can either be directly controlled, for example by means of a pressure of the cushion, or operated by servo-control using a power source outside the cushion. These controls may be rigid or operated by means of elements of considerable elasticity.

Thedetector which actuates the control means can be sensitive to the distance between the top wall defining the cushion and the support surface, the pressure of the cushion which depends directly on that distance, the speed at which any of these two parameters vary and even the vertical accelerations of the vehicle caused by the pressure of the cushion. This detector may also combine the indications relating to several of the above parameters.

Finally, the detection device and the control device proper may be one and the same.

The invention will now be described with reference to the accompanying drawings, wherein:

FIGURE 1 is a partial and diagrammatic vertical section of a platform supported by at least one fluid cushion and provided with a device according to the invention;

FIGURE 2 shows in the same manner a modification actuated by a compressed gas for feeding a carrying cushion;

FIGURES 3 and 4 illustrate two diflerent embodiments of the device in FIGURE 2, in the case of FIGURE 4 in part only, and

FIGURE 5 shows a second modification actuated directly by the vertical accelerations of the platform.

In the drawings, 1 is a platform to the bottom of which is secured at least one deformable skirt 2 defining, with the platform proper and the support surface 3, a fluid cushion 4 fed by a conduit 5 through which the carrying pressure fluid arrives. This fluid escapes outwards under the free bottom edge 2a of the skirt. It is usually compressible.

The fluid forming the carrying cushion 4, which is assumed to be compressible, is, of course, subjected to rapid variations in pressure within the skirt 2 when the support surface 3 is irregular. This deformable skirt has a certain amount of elasticity and its volume varies somewhat when the pressure of the cushion varies. The deformable skirts shown in the drawings for the sake of simplicity can be made of fabric, preferably made impermeable by coating, so as to reduce their extensibility without eliminating it entirely, but the invention naturally includes carrying cushions defined laterally by a highspeed fluid curtain, and such curtains are much more deformable than a skirt subjected to the influence of the internal pressure of the cushion.

FIGURE 1 shows an embodiment of the invention illustrating its principle. The wall of the platform or the vehicle defining the cushion 4 at the top is rigidly connected to a cylinder 6a in which a piston 6b can slide, this piston being rigidly connected by a rod 7 to a doubleaction hydraulic jack 8. Two pipes 9a, 9b connect this jack to a distributor 10. The distributor rod is rigidly connected to a diaphragm 11 which is sensitive to the pressure in the carrying cushion 4, and to a linkage 12 which can comprise a spring 13 and is likewise rigidly connected to the piston of the jack 8. This arrangement is completed by rendering displaceable the articulation 14 of the lever 12 and by fitting on the pipes 9a, 9b of a multi-way tap shown diagrammatically by 28, whereby the flows of the pipes ending on either side of the piston 8 can be reversed, so as to reverse the displacement direction of the piston 6b which corresponds to a given direction variation of the pressure of the cushion 4.

The distributor 10 is fed with pressure fluid by a pump 24 which pumps this fluid into an accumulator 26 from a tank 25.

With the arrangement adopted, in which the motive fluid at a high pressure P arrives at the center of the distributor 10, any increase in the internal pressure of the carrying cushion 4 moves the distributor 10 upwards, so that the pressure P acts at least partly above the piston of the jack 8, so as to'lower the piston 6b and reduce the total volume of the cushion 4. This volume comprises the space limited laterally by the cylinder 6a and at the top by the piston 6b, and communicating with the cushion, without substantial loss of pressure, by the wide orifice formed by the bottom section of the cylinder 6a.

Patented Sept. 12, 1967' Conversely, any chance reduction in the pressure of the cushion, which would naturally tend to reduce the volume of the skirt 2, would according to the invention be sensed by diaphragm 11 and cause distributor 10 to move downwards, applying pressure P under the piston of jack 8, thereby raising the latter as well as causing the piston 6b to rise so as to compensate and even exceed the initial tendency of volume reduction. Calculations show that the combination with a fluid cushion 4 of the device described in principle generally has little effect on the characteristic frequency of the vertical oscillation of the fluid carrying cushion but makes it possible to reduce the amplitude of the vertical displacement of the platform 1 to the resonance and consequently the accelerations to which this platform is subjected.

It suflices to modify the characteristics of the servocontrol 8 to 13, for example by displacing the articulation 14 and even reversing the flows of the pipes 9a, 9b

, by proper actuation of multi-way tap 28, so that, for a given direction of variation of the pressure of the cushion, the direction of displacement of the piston is reversed, so as to vary rapidly and within a wide range the dynamic characteristics of a cushion 4 defined by a given skirt 2. This enables a skirt mock-up to be given mechanical characteristics that are dynamically similar to those of a projected skirt of different dimensions, and also enables the stability range of such a mock-up and the vehicle it represents to be investigated with ease. The calculations show that such a device will reproduce the dynamic characteristics of a vehicle and a mock-up without its being necessary to operate the mock-up in a medium whose pressure would be different to atmospheric pressure, and this makes experiments much easier. As variations of the pressure of the cushion 4, those of the distance separating the platform 1 from the support surface 3 (or the leakage level between the said surface and the edge 2a of the skirt), and finally the vertical accelerations of the platform are concomitant, the diaphragm 11 can be replaced by a feeler in contact with the ground, or even by a weight. The servo-control of the piston 6b may of course also be made sensitive to one of the differential coefficients of the parameters that have just been listed.

FIGURES 2 and 4 shown an embodiment in which the motive fluid of the deformable wall element enabling the total volume of the fluid carrying cushion 4 to be influenced is the same as the fluid that feeds the cushion. A restriction 15 is disposed in the feed conduit so that the pressure upstream of the restriction is applied to at least part of this deformable element which plays a part similar to that of the piston 6b in FIG. 1. In FIG. 2, this element is a double bellows closed by a plate 16b articulated on a hinge 16a, part of which element 17b is subjected internally to the pressure upstream of the restriction and externally to atmospheric pressure, while the other part 18b is subjected internally to the latter and externally to the pressure in the cushion 4. A spring 19!) serves to balance the bellows with respect to the pressure forces under normal operating conditions of the platform 1.

FIGURE 3 shows a device similar to the one in FIG- URE 2, but in this case the bellows are replaced by a sliding double piston.

FIGURE 4 shows similarly, although only in part, a device in which the sliding double piston is replaced by a double piston 17d, 18d with a deformable joint 20 termed a rolling joint. The space above the control piston 17d is fed by a dynamic air intake projecting into the conduit 5. The corresponding elements in FIGURE 2 to 4 are given similar reference numbers, but the letters b, c and d respectively are added.

In every case the stabilizing effect of the devices in FIGURES 2 to 4 is equivalent to the stabilizing effect, described above, of the device in FIGURE 1. When bellows are used (FIGURE 2) the amplification ratio can easily be selected, and as a result power losses due to 4 the restriction 15 can be reduced. The use of a total pressure intake 29 (FIGURE 4) also enables such losses to be eliminated, by making operation without a restriction such as 15 possible.

FIGURE 5 shows a second modification in which a weight 21 moves a diaphragm 23 by means of a lever 22. A spring 27 balances the assembly in normal operating conditions.

This figure shows that if any chance vertical movement of the platform 1 applies an upward acceleration to it,- the inertia of the weight 21 then tends to lift the diaphragm 23 relatively to the platform, i.e. to increase the total volume provided for the cushion 4. According to this embodiment the same element, i.e. the weight 21, serves at the same time as a detector and control element of the variations of the pressure of the cushion 4.

What is claimed is:

1. A ground effect machine designed to move along a bearing surface and having a plenum chamber and closure spaced from said surface, and Wall means projecting in fl'uidti-ght relation from said end closure toward said surface to partially bound therewith a plenum chamber in which a pressure fluid cushion may be formed, said wall means ending in a free end adjacent to said surface but spaced therefrom by an average distance which varies during operation of the machine, said end closure defining an end wall of said plenum chamber opposite to said bearing surface, whereas said projecting wall means defines a lateral wall of said plenum chamber, means for introducing into said chamber a fluid under pressure, wherein the improvement comprises a movable wall member separate and distinct from said wall means but cooperating therewith and with said end closure in defining the volume of said plenum chamber whereby displacement of said movable wall member causes corresponding variation in the plenum chamber volume, and means associated with and movably supporting said wall member in substantially fluidtight plenum chamber boundin-g relation throughout the effective range of displacement of said wall member to Vary said plenum chamber volume whereby said movable wall member remains in fluidtight, plenum chamber volume defining condition throughout said effective range of displacement thereof.

2. A ground effect machine as claimed in claim 1, wherein said movable wall member comprises, in part, a cushion bounding surface which, in association with said end closure, defines an end wall of said plenum chamber opposite to said bearing surface.

-3-. A ground effect machine as claimed in claim 1, further comprising wall member control means responsive to cushion fluid pressure for positively displacing said movable wall member to vary said plenum chamber volume inversely relative to changes in said cushion pressure.

4. A ground effect machine as claimed in claim 3, wherein said control means comprise a diaphragm res'ponsive to said cushion fluid pressure, a distributor valve under the control of said diaphragm, and a hydraulic servo-control system under the control of said distributor valve and acting on said movable wall member.

5. A ground effect machine as claimed in claim 3, wherein said control means comprises a weight movably carried on said machine so as to be responsive to said accelerations thereof, said weight being associated with said movable wall member to move same in response to said accelerations.

'6. A ground effect machine as claimed in claim 1, further comprising wall member control means responsive to cushion introducing fluid pressure for positively displacing said movable wall member to Vary said plenum chamber volume inversely relative to changes in said supply pressure.

7. A ground eflfect machine as claimed in claim 6, wherein said means for introducing a fluid under pressure comprise a presure fluid supply pipe opening into said plenum chamber, and said control means comprises a a total pressureintake projecting into said supply pipe restriction in said pipe to create a pressure drop, and an and commufllcatlng Wlth Said movable Wall memberoperative connection extending from a point of said pipe References Cited 3332:1321 vgeflnsegi Ifqjgiction and communlcating with said 5 UNITED STATES PATENTS 8. A ground effect machine as claimed in claim 6, ggE wherem said means for introducing a fluid under pres- 12331692 2/1966 Guienne sure comprise a pressure fluid supply pipe opening into said plenum chamber, and said control means comprises HARRY Primary Examiner- 

1. A GROUND EFFECT MACHINE DESIGNED TO MOVE ALONG A BEARING SURFACE AND HAVING A PLENUM CHAMBER AND CLOSURE SPACED FROM SAID SURFACE, AND WALL MEANS PROJECTING IN FLUIDTIGHT RELATION FROM SAID END CLOSURE TOWARD SAID SURFACE TO PARTIALLY BOUND THEREWITH A PLENUM CHAMBER IN WHICH A PRESSURE FLUID CUSHION MAY BE FORMED, SAID WALL MEANS ENDING IN A FREE END ADJACENT TO SAID SURFACE BUT SPACED THEREFROM BY AN AVERAGE DISTANCE WHICH VARIES DURING OPERATION OF THE MACHINE, SAID END CLOSURE DEFINING AN END WALL OF SAID PLENUM CHAMBER OPPOSITE TO SAID BEARING SURFACE, WHEREAS SAID PROJECTING WALL MEANS DEFINES A LATERAL WALL OF SAID PLENUM CHAMBER MEANS FOR INTRODUCING INTO SAID CHAMBER A FLUID UNDER PRESSURE, WHEREIN THE IMPROVEMENT COMPRISES A MOVABLE WALL MEMBER SEPARATE AND DISTINCT FROM SAID WALL MEANS BUT COOPERATING THEREWITH AND WITH SAID END CLOSURE IN DEFINING THE VOLUME OF SAID PLENUM CHAMBER WHEREBY DISPLACEMENT OF SAID MOVABLE WALL MEMBER CAUSES CORRESPONDING VARIATION IN THE PLENUM CHAMBER VOLUME, AND MEANS ASSOCIATED WITH AND MOVABLY SUPPORTING SAID WALL MEMBER IN SUBSTANTIALLY FLUIDTIGHT PLENUM CHAMBER BOUNDING RELATION THROUGHOUT THE EFFECTIVE RANGE OF DISPLACEMENT OF SAID WALL MEMBER TO VARY SAID PLENUM CHAMBER VOLUME WHEREBY SAID MOVABLE WALL MEMBER REMAINS IN FLUIDTIGHT, PLENUM CHAMBER VOLUME DEFINING CONDITION THROUGHOUT SAID EFFECTIVE RANGE OF DISPLACEMENT THEREOF. 